1. Field of Invention
This invention relates to heat transfer apparatus, particularly for heating or cooling pipes or like objects via a fluid medium disposed within a heat transfer assembly mounted externally on the pipe. The term "pipe" as used herein includes tubes, conduits or other members, the contents of which is to be heated or cooled by the heat transfer element.
2. Description of Prior Art
U.S. Pat. No. 1,318,237 disclosed a double walled radiator structure for heating liquids as part of an apparatus for radiant heating for homes or rooms. U.S. Pat. Nos. 3,834,458; 3,949,189; 3,971,416; and 4,031,611 owned by the common assignee of the present application disclosed heat transfer assemblies and methods for making the same which generally included a heat transfer element bonded or mounted in heat exchanging relationship to the pipe or conduit using a heat transfer material or mechanical mounting means. Likewise, U.S. Pat. Nos. 4,123,837; 4,152,577 and 4,203,186 disclosed methods of enhancing heat transfer between the heating or cooling elements and the pipe to be heated or cooled. All of these prior patents were addressed primarily to improvements in the heat exchanging relationship between the heating or cooling element and the pipe which was to be heated or cooled. In each of the prior art methods or apparatus, it was contemplated that the heat tracing element, such as a steam tracing tube or an electric resistance heater would be attached to the pipe and trace the path of the pipe to its extremities thereby providing controlled heat or cooling to the pipe system. In past steam or fluid tracing temperature control methods and apparatus it was necessary to separately mount a return conduit to return the heating or cooling fluid from the extremities of the pipe system back to a fluid reservoir located at the central point of the heat traced system. This requirement was particularly undesirable in applications where it was not possible to mount the return conduit adjacent and parallel to the heat tracing conduit making it necessary to mount the return conduit on the opposite side of the pipe being heated or cooled, or at some other even less desirable location away from the pipe. In any event, providing such a return pipe increased the labor and materials costs to install the heat exchange system.